OBJECTIVES: The overall objective of this proposal is to study the biological processes regulating the growth and regression of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in rats. Most DMBA-induced mammary tumors are hormone-dependent and their growth or regression is regulated by the host's endocrine status. This proposal is based on the principle that any tissue growth is a result of a net gain of synthesis over tissue degradation. Thus tissue synthesis and degradation play equally important roles in tumor growth. The following subjects are the areas of my interest for the period proposed: (1) Differential and synergistic roles of estrogen and prolactin on protein and DNA synthesis in DMBA-induced mammary tumors. (2) Interrelationship between synthesis and degradation processes in growing and regressing tumors. (3) Whether or not tumor regression involves processes of active synthesis. METHODS OF PROCEDURES: (1) Multiple syngeneic transplantation of mammary tumors. (2) Synthesis of specific proteins induced by estrogen and/or prolactin in mammary tumors. (3) Synergistic and differential effects of estrogen and prolactin on mammary tumors as assessed by leucine and thymidine incorporation. (4) Prevention of mammary tumor regression by non-hormonal agents. (5) Changes in distribution patterns of mRNA in regressing mammary tumors. (6) Determination of activities of cathepsin D and acid RNase in regressing tumors. (7) Effect of an inhibitor for adenylate cyclase, phosphodiesters, on tumor regression--role of cyclic AMP. (8) Release and retention of radioactivity in regressing and growing tumors pre-labelled with 3H-leucine.